1. Field of the Invention.
This invention relates to timepieces with a quartz watch movement and an electrically controlled sound generator, more particularly to such movements having sizes adapted to wrist-watches, and to sound generators which can also be used in alarm wrist-watches.
2. Description of the Prior Art.
The manufacturers of quartz watches endeavoured to reduce the current consumption in order to extend the life time of the batteries as much as possible. Thus, with the known movements manufactured nowadays the driving moment of the seconds hand is about three Micronewtonmeters.
To provide a watch with a sound generator which shall become operative at a time adjustable in advance, a switch must in any case be inserted between a member moving in synchronism with the hour hand and another member associated with the indicator displaying the time at which the sound generator will become operative. Some known switches are adapted to fulfil these conditions. With the most frequently used switches, one contact pole of the switch rotates together with the hour hand. That pole is located at the end of a radial spring arm which presses it against the plane surface of a disk made of conducting material and carrying the other contact pole of the switch. That plane surface is insulated except along a radial segment constituting said other contact pole, which is reached by the end of the spring arm when the sound generator has to become operative.
To balance the reaction on the piece, to which the spring arm is anchored, and which is due to the pressure of the spring arm against the disk, that arm is formed on the opposed side of the anchoring point with a tail portion also pressing on the disk, but being shorter than said arm, to avoid contact with the switch pole on the disk.
A spring arm balanced in that way can, however, not be mounted in a quartz watch movement as manufactured nowadays, because its friction against the disk overbalances the driving moment of the hands. Consequently, the watch would stop.
A switch is, however, also known, with which the contact pole rotating together with the hour hand is formed at the end of a spring arm extending along an arc of a circle and pressing that contact pole radially against the cylindrical edge of a collar of insulating material mounted on a metal tube provided with a nose flush with the periphery of the collar to constitute the other contact pole of the switch (Swiss Pat. No. 495,006).
Although the frictional moment due to the pressure exerted by the circular spring arm against the collar, with these known switches, is, as a rule, smaller than that due to the radial arm of the most often used known switches, because the friction point is nearer to the axis of rotation, that frictional moment is still too important for the quartz watch movements manufactured nowadays, since said circular arm is too rigid. It is, indeed, formed by stamping a thin metal sheet and is substantially wider than thick, so that it is bent in a plane parallel to the large side of its cross-section. Thus, a small displacement of its end from its position of rest in a radial direction already produces an important restoring force. Due to the manufacturing tolerances such a switch cannot be produced in series while warranting, on the one hand, a sufficient pressure when the switch is on, and, on the other hand, a moment of friction clearly smaller than the moment driving the hands.
The circular spring arm of the known switches having just been considered could be made more supple by disposing the long side of its cross-section in a direction parallel to the axis of rotation of the hands. Mounting such a spring would, however, excessively increase the cost of the switch.